The present invention generally relates to electric heaters and, more particularly, to heaters, such as electric water heaters, employing over temperature shut off controls.
Electrically powered water heaters are commonly employed to heat a supply of water for use in jetted bathtubs, spas/hot tubs and other heated water applications by heating water flowing through a vessel. Electric water heaters typically include an electric powered heating element arranged in a heat transfer relationship with the water flowing within the vessel. In many conventional flow-through water heating systems, a thermostat is disposed within the hollow of the vessel or the tub to sense the temperature of the water, and the heating element is generally controlled based on the sensed water temperature so as to maintain a desired water temperature. One example of a water heater is disclosed in U.S. Pat. No. 6,080,973, the disclosure of which is hereby incorporated by reference.
Conventional electric water heaters employed in jetted bathtubs and spas/hot tubs are generally controlled in response to the sensed water temperature to maintain a user selectable water temperature in the heated water tub. In most jetted bathtubs, a maximum upper temperature limit of about 104xc2x0 F. is typically established according to industry standards. In addition to controlling the heating element to achieve the selected water temperature, it is also desirable to ensure adequate operation of the water heater to prevent an excessive over temperature condition (i.e., overheating) and problems that can arise therefrom. For example, in the event that a failure occurs in the heater controls, the water temperature may exceed the maximum upper temperature limit. The water heater may overheat quickly when there is an inadequate amount of water present in the heater vessel due to an abnormally low water level. Advanced overheating may also occur when there is inadequate water flow through the heater vessel such as may be caused by the failure of a water pump or other water flow restriction.
In order to prevent the presence of an excessive over temperature condition, many conventional water heaters are generally equipped with a temperature actuated shut off device that discontinues power supplied to the heating element when a predetermined upper temperature limit is reached. Conventional temperature-based shut off devices include a snap disc thermal switch connected in series with the power input of the electrically operated heating element. The snap disc thermal switch is designed to switch from a closed position to an open position to open circuit the power line supplying electric current to the heating element upon detecting a predetermined upper temperature limit of about 117xc2x0 F., according to one example. Some industries, such as the jetted bath tub and spa/hot tub industry, have established a requirement to also equip the water heater with a manually depressible reset button, and further require that a user must depress the reset button to reset the heater in order to allow the heater to be energized following an over temperature shut off. Typically, the reset button is located remote from the heated water tub, and thus requires that the user take additional action to reset the heater.
While it is desirable to equip heaters with over temperature shut off protection, there exist certain conditions where a false over temperature determination may occur. For example, if a user fills a spa/hot tub with excessively hot water having an elevated temperature above the upper temperature limit, the snap disc thermal switch may be tripped which, in turn, locks out (shuts off) use of the heater prior to the heater being energized, thus requiring that the user manually depress the reset button to reactivate and allow the heater to subsequently be energized. Therefore, it is desirable to provide for a heater control system that provides over temperature protection and yet reduces or minimizes the presence of false over temperature heater lockout events.
In accordance with the present invention, a heater having a shut off device is provided which prevents false over temperature lockouts. According to one aspect of the present invention, the heater comprises a body having walls defining a volume for holding material, a heating element thermally coupled to the body for heating material within the body, and a temperature sensor for sensing temperature of the material. The heater also has a shut off switch for shutting off the heater when the sensed temperature of the material exceeds a predetermined maximum temperature limit, and a manually actuated reset input for generating a reset signal to allow the heater to be turned on. The heater further includes a controller coupled to the shut off switch and the reset switch, wherein the heater is required to be reset by the reset input when an over temperature event is determined, and wherein the controller determines the presence of a false over temperature event and overrides the need to reset the heater during the false over temperature event.
According to another aspect of the present invention, a heater having a temperature sensitive shut off switch is provided. The heater includes a body having walls defining a volume for holding water to be heated, and an electric heating element thermally coupled to the body for heating water within the body. The heater also has a temperature sensitive switch, such as a snap disc thermal switch, connected in series with the heating element for sensing temperature of the water and shutting off electrical power supplied to the heating element when the sensed temperature of the water exceeds a predetermined maximum temperature limit. The heater further includes a controller connected to the temperature sensitive switch for monitoring voltage potential applied to the temperature sensitive switch and determining whether a failure of the heater has occurred as a function of the monitored voltage potential.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.